drbd: Consistently use block_id == ID_SYNCER for checksum based resync and online verify

DRBD_MAGIC has nothing to do with block ids and the funny values
computed were not actually used, anyway.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index d499aa6..5ed9619 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -341,6 +341,10 @@
 	e->size = data_size;
 	e->flags = 0;
 	e->sector = sector;
+	/*
+	 * The block_id is opaque to the receiver.  It is not endianness
+	 * converted, and sent back to the sender unchanged.
+	 */
 	e->block_id = id;
 
 	return e;